A probiotic supplement might not be as good for your gut as you think

The gut microbiome is the name for the trillions of bacteria and other microbes inhabiting the digestive tract, and it's increasingly recognised as a foundation of good health.

So how do you improve your gut microbiome? Probiotics are touted as one solution — they're live "good" microorganisms that, in theory, colonise the gut after they're ingested and boost overall health.

But while probiotic supplements make sense on paper, new Israeli research bolsters the theory that they don't actually work so well in practice because of the unique differences between everyone's gut microbiomes.

A team from the Weizmann Institute of Science recruited 25 volunteers to test how well probiotic supplements — the kind you'd find in a supermarket — actually colonise the gut.

After the volunteers had their gut microbiomes analysed, half took a probiotic supplement and half took a placebo. Both groups were tracked for several months.

The study, published in the journal Cell, revealed some volunteers had a "permissive" gut microbiome where the probiotics easily took hold — yet others had a "resistant" microbiome where the opposite proved true.

"Surprisingly, we saw that many healthy volunteers were actually resistant in that the probiotics couldn't colonise their GI tracts," said the study's senior author, immunologist Eran Elinav, in a statement.

"This suggests that probiotics should not be universally given as a 'one-size-fits-all' supplement. Instead, they could be tailored to the needs of each individual."

A novel aspect of the study is that the participants didn't only have their gut microbiomes analysed via faecal samples — as is standard for a lot of gut research — but also via endoscopies and colonoscopies.

These added tests indicated the microbial composition of faeces doesn't necessarily match up with the actual microbial composition inside the gut. Or, to put it more bluntly, just because you're pooing out particular microbes doesn't mean there are any left inside.

"Although all of our probiotic-consuming volunteers showed probiotics in their stool, only some of them showed them in their gut, which is where they need to be," added computational biologist Eran Segal, a co-author of the study.

Twenty-one study participants took a course of antibiotics that wiped out their gut microbiome. Some of them took a probiotic to test whether it would bring their microbiome back online faster.

To the researchers' surprise, the supplement had the opposite effect: it took months for their microbiomes to return to its pre-antibiotic state, much longer than a group who took no probiotic and let their microbiome recover by itself.

FYI, a third group was treated with samples of their healthy faecal microbiome taken before the antibiotics — a so-called poo transplant. It sounds gross, but it worked: their microbiomes recovered within days.

"Replenishing the gut with one's own microbes is a personalised Mother Nature-designed treatment that led to a full reversal of the antibiotics' effects," observed Elinav.